This invention relates to functional colloids and a method for their manufacture.
Colloids have been known for a long time. They can arise, for example, via sol-gel technique, or in natural processes, such as in bodies of water and during condensation processes in the gas phase. It is typical for such colloids that they are only stable in an aqueous solution if prevented from aggregating via stabilizing factors. Aggregation can be initiated through interactions between the colloid particles, e.g., via van-der-Waals forces, hydrogen bridges, hydrophobic interactions, dipole-dipole-interactions or chemical bonds. Given the extremely large surface, the tendency toward aggregation is particularly great. Colloidal particle normally have dimensions not exceeding 0.2 μm.
In general, colloid stabilization takes place via a corresponding zeta potential, i.e., the formation of a dual charge cloud around the colloid. This can be caused by a varying electron affinity, or a charging of particles with ions or electrons, e.g., by setting the pH value. However, it can also take place via the agglomeration of specific molecules on the surface, e.g., via the agglomeration of humic acid in natural bodies of water. However, all of these processes assume that the colloids have been generated by a preceding reaction, and that conditions leading to such a stabilization have been established in the environment of the colloid.
While other methods for manufacturing small particles, e.g., high-energy milling, shatter the crystalline structure down to nanoscale proportions, they cannot prevent subsequent aggregation. Such aggregated particles, which are in part also manufactured via targeted condensation from gas phases, can only be deaggregated under specific conditions. For example, metal particles have been successfully dispersed in oil, since the oil can shift between weakly interacting metal surfaces. However, weakly interacting metal surfaces are only obtained if the metal particles are fabricated in a high vacuum, i.e., under ultra-pure conditions, so that no oxide surface is formed. If this is not the case, it becomes practically impossible to disperse the particles any longer. In the aforementioned high-energy milling process, a redispersion to primary crystallite size is hence no longer possible.
As shown above for metal particles redispersible in oil, such systems can only be controlled from a process standpoint in exceptional cases. Process control requires a method that sets the colloid particles during manufacture in such a way that they satisfy the respective process-related requirements. In this way, it would be possible to impart the desired properties or functions to the colloid particles during manufacture. For example, it would be possible to stabilize, compatibilize, intertize or reactivate the colloid particles relative to the environment.
Commercially available milling aggregates commonly only make it possible to obtain particles in the submicrometer range, and even that only with so-called milling aids, which prevent freshly generated fractured surfaces from recombining again. Comminution to colloidal dimensions, in particular to a range of 0.002 to 0.05 μm, is generally not possible.
The object according to the invention was now to fabricate colloids that exhibit an outstanding stability relative to aggregation, wherein the colloid particles can be extremely small (preferably under 0.2 μm, in particular under 0.05 μm), and the properties or functions of the colloid or colloid particles can be adjusted to the respective requirements.